Motor vehicles, as presently manufactured, are equipped with systems for defogging and deicing windshields. Generally these systems depend upon heat generated in the internal combustion engine of the vehicle and transferred to the engine's cooling system to be blown as warm air across the interior of the windshield to accomplish the defogging and deicing. In such a case, of course, it is readily apparent that there is a period of time between the starting of an engine of a vehicle and the time that sufficient heat is being generated in its cooling system in order to provide a defogging and deicing of the vehicle's windshield. Depending upon the exact temperature conditions and the time the vehicle has been sitting idle without its engine running, the period of time before sufficient heat is available to accomplish this defogging and deicing function can be up to 10 minutes or more.
In view of the fact that there can be a rather lengthy delay before the present day motor vehicles heating and defrosting systems can clear a windshield, automotive designers had been attempting to design systems which generate heat from electrical energy to accomplish a relatively rapid defrost and deicing of a vehicle windshield. Such an electrically heated defrosting and deicing system generally would be independent of the normal heating and defrosting system contained in the motor vehicle.
Many different systems have been proposed for accomplishing this rapid defrost and deicing function, including the placement of an electrically conductive transparent coating on the windshield and the embedding of fine wires in a laminating interlayer of the windshield. To the best of our knowledge, there are no such rapid defrost and deicing systems in vehicles which are currently sold in the U.S. market, except windshields which are made in accordance with the method of our invention which are to be introduced into the U.S. market in 1986 on vehicles produced and sold by Ford Motor Company, the assignee of this application. We believe that no previous systems have been introduced because of the relatively high cost of such systems, and also because of electrical problems associated with installation of such a system in a vehicle windshield such as found in today's automobiles. The method set forth by us in this specification is one which produces an electrically heatable windshield of laminated construction which is of relatively moderate price and which can be rapidly defogged and deiced by application of electrical energy thereto in a period of time substantially shorter than can be achieved by defogging and deicing of the windshield using the normal defogging and deicing system of that vehicle.
A search on the subject matter of this disclosure was conducted by Mr. Kevin J. Ramus, one of the inventors herein, in the U.S. Patent and Trademark Office. Mr. Ramus did not uncover in his search any patents which appear to be relevant to the subject matter of this specification.